PROJECT SUMMARY/ABSTRACT Antigen-experienced memory T cells constitute a diverse, heterogeneous population of immune cells that is generated throughout life in response to a variety of pathogens, vaccines, allergens, self-antigens and other environment factors. In fact, as we age, generation of new nave T cells diminishes and memory T cell populations dominate the repertoire. Thus, the basic mechanisms that regulate the functions of diverse memory T cell populations has broad relevance for a variety of diseases and pathological conditions including vaccine designs, immunotherapy protocols and treatment or prevention of inflammatory or autoimmune disorders. Although the formation and differentiation of memory CD8+ and CD4+ T cells in the circulation has been extensively characterized, the capacity for memory T cells to actively home to and infiltrate tissues where they exhibit their effector functions is less understood. We have recently discovered that memory CD8+ T cells require post-translational O-linked glycosylation of selectin ligands for trafficking to and infiltrating non- lymphoid tissues. Furthermore, we identified that de novo synthesis of core 2 O-glycans is restricted to memory T cells and can be regulated in an antigen-independent manner. However, the basic molecular mechanisms regulating core 2 O-glycan synthesis and trafficking of memory CD8+ and CD4+ T cells during infections are yet to be fully characterized. Specifically, we will 1) determine if different CD8+ T cell populations have the capacity to synthesize core 2 O-glycans and traffic into non-lymphoid tissues, 2) define the molecular and transcriptional mechanisms that regulate core 2 O-glycan synthesis in memory CD8+ T cells, and 3) determine if memory CD4+ T cells require core 2 O-glycan synthesis to traffic into non-lymphoid tissues during either acute or chronic viral infections. Thus, the overall goal of our study will be to identify and characterize the mechanisms regulating the trafficking of diverse memory T cell populations and how this can be enhanced (for host protection) or inhibited (for allergies or autoimmunity).